1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for use in oil and gas wellbores. More particularly, the invention relates to an isolation valve with debris control and flow tube protection.
2. Description of the Related Art
An isolation valve is located as part of the casing string and operated through a control line. The isolation valve is configured to temporarily isolate a formation pressure below the isolation valve such that a tool string may be quickly and safely tripped into a portion of the wellbore above the isolation valve that is temporarily relieved to atmospheric pressure. Thus, the isolation valve allows the tool string to be tripped into and out of the wellbore at a faster rate than snubbing in the tool string under pressure. Since the pressure above the isolation valve is relieved, the tool string can trip into the wellbore without wellbore pressure acting to push the tool string out.
The isolation valve is movable between an open position and a closed position by selectively actuating a flapper valve of the isolation valve. The flapper valve is actuated by the movement of a flow tube in the isolation valve. In the closed position, the flapper valve obstructs a bore through the isolation valve, and in the open position, the flapper valve resides in a flapper valve cavity. Prior designs for the isolation valve can suffer from various disadvantages. One disadvantage of prior designs is that debris and mud may enter the flapper valve cavity during operation of the isolation valve. The debris and mud may inhibit the function of the flapper valve and thereby affect the opening and/or closing of the isolation valve. Another disadvantage of prior designs is that an end of the flow tube oftentimes becomes damaged while stripping or tripping the drill string through the isolation valve. The damaged flow tube may subsequently cause damage to the flapper valve as the flow tube moves through the isolation valve. Therefore, there exists a need for an improved isolation valve assembly and associated methods.